The concept of using unprocessed waste toner to modify asphalt is well known to those skilled in the art. U.S. Pat. No. 6,113,681 (Tripathi et al. 2000) describes compositions and methods for making and using toner modified asphalt compositions. Toner is a powder that is specifically formulated for use in photocopiers and laser printers in order to form printed indicia and images on paper. Toner powder is a very fine dust with particle sizes on the order of 8-16 micrometers and there are hundreds of variations in chemistry, particle size, particle shape and color. Toner incorporates a polymer that is melted in order to bind the printed indicia/image to the paper. That polymer may be styrene acrylate, polyester or styrene butadiene. These different toners produce different physical and mechanical properties in asphalt.
The problems associated with using unprocessed waste toner in asphalt are considerable and this likely explains why this additive has not had any commercial impact to date. Some of the problems associated with the effective and commercially viable use of unprocessed waste toner as an asphalt additive relate to form, variability of raw materials, and OH&S issues associated with handling fine powders. Further, unprocessed waste toner only adds plastomeric properties to asphalt. Such properties improve the high temperature performance of the asphalt. More specifically, the unprocessed waste toner additive increases the stiffness of the asphalt to reduce longitudinal rutting and minimize high-temperature induced microcracking of the road surface. Thus, unprocessed waste toner additive tends to increase the life cycle of the roadway at higher ambient temperatures.
However, when one adds a sufficient amount of unprocessed waste toner to asphalt in order to achieve these high temperature performance benefits, one effectively degrades the low temperature performance of the asphalt. More specifically, at lower ambient temperatures, the increased stiffness provided to the asphalt by the unprocessed waste toner additive becomes a detriment. This is because the added stiffness makes the asphalt more susceptible to cracking in response to each freeze-thaw cycle.
The present document relates to compositions of asphalt incorporating modified toner based additives that overcome all known existing issues. The modified toner based additive described herein is made by mixing waste toner powder with gelling clay, reactive agents, elastomers, functional fillers, handling and agglomerating agents, compatibilizers and mixtures thereof. During the mixing and agglomerating process, the toner undergoes frictional heating, shear, sintering, coalescence, fusion and molecular or polymer chain entanglements of the toner particles. In many embodiments the toner powder particles are subjected to polar-polar interaction with other additive components. For example, FIG. 1 illustrates the polar-polar interaction (note dashed line) between a toner particle T and a treated crumb rubber particle R. FIG. 2 illustrates the polar-polar interactions (note dashed lines) between a compatibilizer C and both a toner particle T and a treated crumb rubber particle R. FIG. 3 illustrates the polar-polar interaction (note dashed line) between a toner particle T and an untreated crumb rubber particle R. Thus, as should be appreciated, the toner particles in the resulting modified toner based additive have undergone a physical change that renders them unsuited for use in photocopiers and laser printers but admirably suited for use as an asphalt additive.
The modified toner based additive is in the form of granules, of perhaps 0.1-2.0 mm, with consistent shape and size giving flowable product with superior handling properties as compared to unprocessed waste toner. Furthermore, the moisture content is consistently between 2 and 15 percent by weight and the toner chemistry is homogenized. Further, unlike unprocessed waste toner, the modified toner based additive improves both the high temperature and low temperature performance of the asphalt to which it is added.
More specifically, the plastomeric properties of the polymer (e.g. styrene acrylate, polyester and/or styrene butadiene) from the toner serve to increase the stiffness of the asphalt to improve the high temperature performance of the asphalt as described above. In addition, where the toner is mixed with a material having elastomeric properties, the increases in stiffness are balanced out and a flexibility is imparted to the asphalt at low temperatures so it is able to better resist cracking in response to freeze-thaw cycles. Thus, while unprocessed waste toner improves the high temperature performance of asphalt at the cost of degrading low temperature performance, the modified toner based additive described herein improves both, thereby representing a significant advance in the art. Further it does so in a single additive with the proper proportion of toner based plastomer and elastomer to provide the best results. Such a product eliminates human error in on site asphalt mixing and is very convenient to use.
The present document also describes a range of new asphalt and asphalt concrete compositions, made possible with the use of additives at the agglomeration stage, that offer vastly superior features and benefits in asphalt when compared to unprocessed toner.